Transducers of the type RSPUDT are known, e.g., from an article of J. M. Hode, et al., “SPUDT-Based Filters: Design Principles and Optimization”, 1995 IEEE ULTRASONICS SYMPOSIUM, pages 39-50. RSPUDT transducers are used in transversal filters. Filters using such transducers have a low insertion loss.
Designing an RSPUDT filter having a desired transfer function needs an optimization of the distribution of sources and reflectors over the length of a transducer. The piezoelectric substrate material is chosen to achieve a desired bandwidth which is dependent on the coupling factor of the material. Suppression of triple transit signals and a high out-of-band rejection is a question of sufficient resonant structures and the length of the transducer.